Ericsson GM25 GSM Modem & Traffic Monitor


Thread Starter


Hi there.
I'm working in traffic telematics, and use a roadside equipment to measure traffic that is called a "Golden River Marksman 660". The manufacturer states that "it doesn't actually support hardware handshaking" and "expects the CTS signal to be held high by the modem.
I have been trying to make a telemetry system in order to connect to a remote site via a GSM modem (in this case Ericsson GM25 modules). The thing is, although I don't have any problems talking to the machine via RS-232 directly from a PC with 9600-8-N-off, and hyperterminal, when I use a modem in between I get no answer, even if I program "full transparency" on the modem (via AT commandS), that is:
-no flow control
-ignore DTR line
-no carrier detect
-no echo (ATE0Q1)
-CTS always on
-DSR always on
-comms between modem/monitor at 9600
-auto-answer, of course.

Can anybody give me a hint?

Paul Vosselmans

Is the number you're calling a data number ( at least that was my initial problem when trying
to setup a teleservice connection ) ? Here in the Netherlands each GSM has three numbers : voice , fax and data.


Paul Vosselmans
My experience with NOKIA type handphone may help you as I have the same with hyper cannot work with a serial program.
What I did to make is work is to send only once characters wait for the character to be echo back before sending the next character

It solve the problem for me. Try this. What I did was, send the first character, then use the echo character interrupt to send the next char, until the output buffer is empty. Slow, but it works.

Derek SK Chan
HP: (65) 9788 4248
System Engineering Design &
Consultancy Services
32 Ang Mo Kio Industrial Park 2
Sing Industrial Complex, #04-06
Singapore 569 510
Tel: (65) 482 1719, Fax: (65) 482 1759
yep, I am using a correct number for data comms. I checked that one early on, since initially I was only getting a voice answer, but now I can correctly connect in data mode.
How do I "use the echo character interrupt to send the next char"? I will have to investigate that bit. thanks.

I've just seen your e-mails by chance . Did you get any answers? We have a technical support department that will be able to help you if you want. Mail me back if you want some support. Best Regards Andrew Suttle. [email protected]

I'm using the module GM25 and now I seem to have a little problem. I use two modules to communicate with each other. I'm dialing the number of module 1, which will answer automatically (ATS0=2), and indeed after a while I get the message
"CONNECT 9600". So I suppose I really have a connection after I got the message, but I don't know how to go further now. At that point I want to send a file from module 1 to module 2 but how can this be done ? Are there still some AT
commands I have to use or should I go to an higher layer protocol (something like Kermit or FTP perhaps) now ?

Thanks in advance, greetings Bart.

Once you got the Connect Message the connection is established. Then you have so called circuit switched data connection and any further character/byte you sent will be directly delivered to the other side. So if you want to exchange for examples files you may directly send the file on the one side by sending byte after byte using the same method you used for sending the AT commands. On the other side you will be able to receive all the data, as you received responses of AT commands. Thats it. In fact it means that you normally have to establish some home grown protocoll so that each side knows
what is going to happen, e.g. intent to send a file, received file, etc.

Yours, torsten.